1. Field of the Invention
The invention relates to a corrosion inhibited antifreeze composition useful as a coolant in a heat exchange system such as the cooling system of an internal combustion engine.
2. Prior Art
Antifreeze concentrate compositions adapted to be diluted with water and used as coolants for internal combustion engines generally contain a major amount of a water-soluble alcohol, about 0.5 to 5 percent by weight of additives to inhibit corrosion and foaming during use, and the balance water. The alcohol can be methanol, ethylene glycol, diethylene glycol, glycerol, etc. The additives besides metal corrosion inhibitors and antifoam agents can include a water-pump lubricant. As a consequence of the wide variety of metals utilized in contact with the cooling system compositions in an internal combustion engine, a wide variety of inhibitors have been proposed for use in cooling system compositions containing an alcohol. This is because no one inhibitor has yet provided protection for all of the various metals in contact with the cooling system liquid. Examples of prior art corrosion inhibitors include inorganic compounds such as alkali metal phosphates, borates, molybdates, arsenates, arsenites, nitrates, silicates, nitrites, and chromates, as well as various organic compounds such as mercaptobenzothiazole, benzotriazole, piperazine, ethylene diamine tetracetic acid and the reaction product of phosphoric acid or boric acid and an alkanolamine.
Recently, efforts have been made to eliminate the alkali metal nitrates and nitrites from antifreeze compositions as well as amine-corrosion inhibitors such as triethanolamine and diethanolamine. This is because of the possible formation of the carcinogenic nitrosamines which can be formed by the reaction of a second amine and a nitrite. The elimination of nitrates is believed desirable since upon reduction, nitrites are formed which could in turn react with a secondary amine to form the undesirable nitrosamines. The elimination of nitrites and nitrates from antifreeze compositions generally results in greater susceptibility of the metals in contact with such antifreeze compositions to corrode and this is particularly true of iron and steel. Heretofore, antifreeze compositions have been prepared free of alkali metal nitrites and nitrates by incorporating a corrosion inhibitor prepared by the reaction of boric acid, phosphoric acid and a mono-, di- or trialkanolamine together with an alkali metal mercaptobenzothiazole. Such compositions, however, have not been entirely satisfactory with respect to the inhibition of corrosion of cast iron and steel in contact with ethylene glycol-based antifreeze compositions as indicated in U.S. Pat. No. 3,350,316. Triethanolamine salts of mono- and di-nonylphenol (ethoxylate) phosphate acid esters are also known from U.S. Pat. No. 3,422,166 as corrosion inhibitors for use in metalworking operations such as the working of aluminum, iron and steel.
Imidazolines are known for use in aqueous systems as corrosion inhibitors for metals in contact therewith from U.S. Pat. No. 4,000,079. Phosphoric acid and an alkanolamine as well as sodium nitrite and sodium nitrate are disclosed as conventional corrosion inhibitors to be used therewith. However, the imidazolines of the latter patent are structurally dissimilar to those disclosed herein. Water-soluble corrosion inhibitors for metals, particularly ferrous metals, in contact with petroleum oil well fluids are disclosed in U.S. Pat. No. 3,758,493. These are produced by reacting water-soluble aliphatic mono- and dicarboxylic acids with a substituted imidazoline. Such compounds are structurally dissimilar from the imidazolines disclosed herein.
In U.S. Pat. No. 3,932,303, the corrosion of metals by oxygen-bearing waters is disclosed as inhibited by a combination of an alkanolamine phosphate ester and at least one member selected from the group consisting of phosphates, phosphonates, and low-molecular weight polymers such as polyacrylates and polyacrylamides. Where both steel and copper are present in the same system, compounds of benzotriazole or mercaptobenzothiazole are added to the system containing the above corrosion inhibitors.